1. Field of the Invention
This invention relates to replaceable development stations for use in electrostatographic machines having automatic developer mix monitors.
2. Description of the Prior Art
Electrostatographic machines generally use a two-component developer mix comprising a toner powder and a magnetizable carrier material. During the use of the apparatus, toner powder has to be replenished in a quantity necessary to compensate for the consumption of toner powder used for the development of images. Various automatic toner replenishment systems are known wherein a signal representative of the detected concentration of toner powder in the developer mix is compared with a reference signal corresponding to a predetermined reference toner concentration. When the detected concentration is lower than the reference concentration, replenishment occurs.
The reference signal is fixed during manufacture, but re-setting in the field is often necessary when the developer mix is changed. U.S. Pat. No. 4,708,458, which issued to Ueda et al on Nov. 24, 1987, discloses a system which, when activated at the time of replacement of the used developer mix with new mix, resets the reference signal. Thereafter, the signal representative of the detected concentration is compared to the reset reference signal.
In some copiers and printers, entire development stations are replaceable when its original supply of toner is exhausted. Commonly assigned U.S. patent application Ser. No. 116,200, now U.S. Pat. No. 4,797,704, filed in the names of L. A. Hill et al on Nov. 3, 1987, discloses a disposable (and therefore, replaceable) development station which is completely sealed after being loaded with developer and toner materials. Accordingly, the useful life of the station is determined by the single supply of toner powder therein.
While the system of previously-mentioned U.S. Pat. No. 4,708,458 for resetting the reference signal at the time of change of the developer mix would be useful with replaceable development stations such as taught by application Ser. No. 116,200, now U.S. Pat. No. 4,797,704, there would exist a risk that an operator would forget to activate the resetting system. This would result in a false reference signal set to the previous development station characteristics.